Great thread, guys, you've taught me some good stuff.
Krush.. when you say "Can you change the location of the nested dimension for a selected handful of DBs and not all of them?"
Couldn't you use a LinearStretch parameter/action to move the dimension while keeping it attached to the object it's dimensioning? The selection polygon would have to encompass the two arrowhead points, but not the node endpoints of the dimension, and then it should relocate the text and arrowheads like you would normally stretch/move a dimension... afaik... I haven't used dimensions within dynamic blocks... but I will be starting to shortly, as I've decided to dimension in model space for our typical details that will be inserted from tool palette.